Thresholds and entry ways have been a significate part of residential homes since the day of the cave man. History indicates that a stone was rolled in front of an entry way in early years to protect the inhabitants from the outside. At one time, animal skins served as an easily operable closure for the residence. Still later, solid doors mounted on hinges were invented. Door structures have remained rather consistent in structure for the past several hundred years.
Over the years the structure of the residence has changed. Early man lived in a cave. Constructed residences also have changed over the years. Early homes were made of weather resistant material, e.g., stones, one piled upon another. Later homes were made of wood that required surface protection such as painting. In recent years low maintenance, e.g., weather resistant material has been used in home sidings. These sidings have generally been vinyl siding. With this recent change to vinyl siding, the door jambs have remained of prefabricated wood structure.
Generally the door structure has included a panel mounted on two or more hinges. The door panel and the supporting hinges are mounted within a casement surrounding the opening in the residence. The door panel has been constructed of a variety of materials such as fancy carved wood, light weight hollow core wood paneling, as well as, impenetrable steel.
The structure surrounding the opening is typically referred to as a door jamb. The door jamb has a threshold which is the structure extending across the bottom side of the opening, and a pair of upright side jambs and a head jamb which are mounted in a rough opening. The rough opening typically is defined by a floor structure at the bottom, a pair of up right dimension lumber supports, i.e., 2×4s at each side of the rough opening and a header across the upper portion of the rough opening. The rough opening will usually include a wall board adjacent to the opening on the inner surface and outside sheeting and perhaps finish siding on the outer side of the rough opening.
A problem has existed in that door jambs have been of wood construction and thus not weather resistant. Attempts have been made to improve the weather resistance of the door jamb by coating the exposed wood door jambs with paint and/or a vinyl or aluminum coating. This has only been partially successful. The paint tends to deteriorate in the weather and the vinyl or aluminum coating tends to separate from the wood leaving the wood exposed to the weather deterioration.
Another problem has commonly been encountered in building residential homes due to variations in the thickness of the wall defining the rough opening. The thickness of the wall depends on the materials used in the construction. For example, the inner wall may be ½ inch dry wall, ⅝ inch dry wall or ⅝ inch dry wall plus ¼ inch wood paneling. The structural lumber used in the wall may be what is commonly referred to as construction lumber e.g. 2/4s or 2/6s. The outer wall structure may be ⅝ inch sheeting, 1 inch wood sheeting, ⅝ inch plywood sheeting, ½ inch plywood sheeting or sheeting of other thicknesses. In addition, the outer siding or finish material may be of various thicknesses. For example: A quarter inch asphalt siding may be used, alternatively, half inch wood board siding may be present. The most popular siding today is vinyl siding. The vinyl siding requires minimal care and upkeep. Vinyl siding is made of any of various polymeric materials. In some instances, insulation is provided within the vinyl siding and in other instances, sheets of insulation are provided between the sheeting and the outer siding.
Thus the thickness of the wall structure will vary depending on the materials selected. This has generally required that the door jamb be modified on site after the wall structure has been put in place. While it may have in the past been desirable to have pre-constructed door jambs, often the pre-constructed door jamb has not been of the appropriate dimensions to fit the desired wall structure. This required that door jamb extenders in the form of strips of wood material be used to provide the desired dimension. Alternatively, the door jambs were cut to a narrower dimension, such as on a table saw.